1. Field of the Invention
The present invention relates to a high-frequency energy supply means, and to a high-frequency electrodeless discharge lamp device.
2. Related Art of the Invention
A high-frequency electrodeless discharge lamp is more advantageous than arc-discharge lamps having electrodes in that electromagnetic energy is easily coupled to the filler, mercury can be eliminated from the filler for discharge emission, and higher luminous efficacy is expected because there is no loss due to the electrode. Since it has no electrodes within the discharge space, no blackening of the internal wall of the bulb occurs due to the evaporation of the electrodes. This extends the life of the lamp to a large extent. Because of these features, a high-frequency electrodeless discharge lamp has actively been studied in recent years as a high-intensity discharge lamp of the next generation.
Also in general discharge lamp devices, since ideal design for luminous intensity distribution can be achieved, by reducing the size of the light source to approach a point light source, the size reduction of plasma arc which is in a light source is strongly demanded. For example, when application to standard liquid crystal video projectors is considered, the size of the plasma arc of about 3 mm or less is required for the optical design for increasing the efficiency of utilization of light emission. In an electrodeless discharge lamp, on the other hand, the size of plasma arc is determined by the inner diameter of the bulb. However, since the size reduction of conventional high-frequency electrodeless discharge lamp devices using resonators are limited depending on wavelengths, they are not suited in application fields which require high-luminance point light sources. In recent years, therefore, a high-frequency energy supply means that can supply a high-frequency resonant electromagnetic field concentrated in a space smaller than the space to which a resonator supplies it has been developed.
Referring to FIG. 10, a technique will be described below based on "a high-frequency energy supply means and a high-frequency electrodeless discharge lamp device" disclosed in Japanese Patent Unexamined Publication No. 10-189270 (now U.S. Pat. No. 6,049,170).
The high-frequency energy supply means disclosed in Japanese Patent Unexamined Publication No. 10-189270 comprises a plurality of side resonators concurrently having an electromagnetic-inductive functional part produced from an annular conductive material and an electric-capacitive functional part consisting of gaps, and has a constitution to supply high-frequency energy required for discharge with the resonant high-frequency electromagnetic field at the center of the group of side resonators consisting of a plurality of annularly arranged side resonators so that the electric-capacitive functional part faces inward. Therefore, it is an object of the present invention to provide a high-frequency energy supply means that can supply a high-frequency resonant electromagnetic field concentrated in a space smaller than the space to which a resonator supplies it, and a high-frequency electrodeless discharge lamp device that uses such a high-frequency energy supply means.
As an example of groups of side resonators, FIG. 10 shows an 8-vane type resonator 102 comprising eight plate-like vanes 105 produced from a conductive material protruded toward the center from a cylinder 104 produced from the same conductive material. The surface of the internal wall of two adjacent vanes 105 and the cylinder 104, and the space produced in between act as the electromagnetic-inductive functional part, and the two protruded parts of vanes adjacent to each other and the gap between them act as the electric-capacitive functional part. An electrodeless discharge lamp 101 is positioned on the center portion of the 8-vane type resonators 102. The high-frequency energy propagated by the high-frequency oscillator means is coupled to the 8-vane type resonator 102 by an electric-field coupling type high-frequency coupling means 103 electrically connected to one of the vanes 105 by caulking or welding. The 8-vane type resonator 102 has been designed so as to resonate at the frequency of the high-frequency energy to be coupled. Thus, energy required for high-frequency discharge is supplied to the electrodeless discharge lamp 101 by the resonant high-frequency electric field E generated at the center portion of the 8-vane type resonator 102.
In particular, when the number of the side resonators is N, if the frequency of the high frequency or the shape of a side resonator is designed so that the group of side resonators is driven in the mode where the phase of a side resonator is shifted by 2.pi./N from the adjacent side resonator, the electric charge of a protruded part has the opposite polarity from the electric charge of the facing protruded part. The resonant high-frequency electric field E generated by this electric charge is oriented to the diameter direction of the center portion of the group of side resonators, and has distribution across the electrodeless discharge lamp 101. When the resonator is operated in the 2.pi./N mode, the strongest electric field is obtained at the center portion where the electrodeless discharge lamp 101 is placed.
The high-frequency coupling means may also be of a magnetic-field coupling type as shown in FIG. 11. In FIG. 11, the end portion of the loop antenna 113 is electrically connected to the cylindrical portion of the 8-vane type resonator 112. A resonant high-frequency electric field E is generated at the center portion of the 8-vane type resonator 112 by the high-frequency magnetic field oscillated from the loop antenna 113. High-frequency discharge energy is supplied to the electrodeless discharge lamp 111 by this resonant high-frequency electric field E.
By the high-frequency discharge energy supply means disclosed in Japanese Patent Application No. 10-189270, plasma arc as small as 10 mm or less may by produced and maintained even by high frequency of 2.45 GHz.
By the use of the above constitutions, however, since the direction of the electric fields is constant when operated in the 2.pi./N mode in order to obtain the strongest electric field, the mode is disturbed if the plasma is dislocated by thermal convection, and the discharge plasma often becomes unstable. Also, since the electric field is deflected in a certain direction, the thermal load of the electrodeless discharge lamp to the wall of the discharge tube deflects the direction of the electric field and is increased.